A screw press has been well known as an apparatus for thickening and dehydrating sludge including organic substances of poor filtration characteristics, the screw press reducing moisture content in dehydrated sludge by adding flocculant to raw slurry including the substances and forming flocs of suspended matter, and recovering filtration surface, which is easily clogged, while rotating a screw provided in an outer cylinder screen. Furthermore, a screw press is disclosed, which is provided with a screw and an outer cylinder screen configured to rotate in opposite directions to each other, and which aims to prevent an excessive load by means of decreasing the speed of an outer cylinder screen by detecting a load with a load detecting device installed in an outer cylinder screen drive motor. (Refer to Patent Document 1).
Furthermore, a control apparatus is disclosed, in which a filtration apparatus that a screw is rotatably provided inside a filter is provided with a supply pressure detecting means, a screw torque detecting means, and a screw-rotational speed control means so that the rotational speed of the screw is controlled using a detected results of the supply pressure detection and the torque detection to thereby maintain the moisture content of a thickened sludge to be constant (refer to Patent Document 2).
As a thickener which is used for thickening raw sludge and the like, a differential rate rotary thickener is disclosed in which an outer cylinder including on the circumferential surface thereof a screen (a filter element), and a screw, which is concentrically located within the outer cylinder, rotate in the opposite direction; and sludge, which is fed into the outer cylinder being disposed substantially horizontally, is thickened using a filtering separation method and discharged while transferring the sludge in the axial direction of the outer cylinder by using the screw (refer to Patent Document 3).
As a control apparatus for a rotary thickener, a centrifugal thickener is disclosed in which a disc-shaped detecting body is submerged in thickened sludge, and a torque detecting apparatus is provided to a drive motor being connected to the detecting body so as to measure the sludge concentration, whereby an amount of feed sludge and the rotational speed of an outer cylinder bowl are adjusted (refer to Patent Document 4). Moreover, a centrifugal thickener is disclosed, in which a viscosity detector and an automatic control means are provided with which, after submerging a rotary wing in the thickened sludge, a detected concentration value detected from rotary torque of the rotary wing is outputted so that the concentration of the thickened sludge is maintained to be constant by controlling a rotation difference (refer to Patent Document 5).
Patent Document 1: Japanese Patent Application Laid-open No. Hei 4-238699 (claim 2, FIG. 1)
Patent Document 2: Japanese Patent Application Laid-open No. 2002-239314 (claim 4, FIG. 1)
Patent Document 3: Japanese Patent Application Laid-open No. 2001-179492
Patent Document 4: Japanese Utility Model Application Laid-open No. Hei 6-25747 (claim 1, FIG. 1)
Patent Document 5: Japanese Patent Publication No. Hei 1-39840 (Scope of Claim, FIG. 5)